removed svd_vad1func, svd_vad2func, svd_vvp2func, and svd_vvp3fund from libsvdfit after discussion with Adriaan, since these functions are not used.
changed all function return codes to non-zero numbers when exiting unexpectedly
added a reference version of adriaans code to the repository --makes it easier for him to see if errors I find are also present in his code.